As such machine tool, a lathe provided with a turret to which a tool unit can be radially attached with respect to an indexing axis has been known. The cited patent document 1 discloses a turret tool post where rotation driving force is transmitted from a driving shaft provided inside a non-pivoting shaft to a rotary tool through an intermediate driving shaft. A direction of the rotation axis of the rotary tool cannot be changed from the original direction that is perpendicular to a pivoting axis of the turret. Accordingly, a secondary machining for a tilted hole would require a special tool unit for every requested angle. An increase in the number of types of the rotary tool unit would increase cost and storage space, and further the machine in size.
A composite machining lathe disclosed in the cited patent document 2 is provided with a tool axis tilting mechanism adapted to change the angle of an axis (a rotation axis) of a rotary tool by tilting a tool support head, thereby eliminating the need of a special rotary tool unit for every tilt angle. In trying to machine a workpiece, rotation driving force is transmitted from a first driving shaft provided inside a turret shaft to a tool through a cylindrical second driving shaft. The first driving shaft is driven by a tool motor at a high speed, and therefore the first driving shaft, the second driving shaft, and the tool are rotated at a high speed. In trying to rotate the tool support head, a pivoting shaft inserted to the second driving shaft and the second driving shaft are connected, and then pivoting driving force is transmitted from the first driving shaft to the tool support head through the second driving shaft and the pivoting shaft, thereby causing the tool support head to be tilted. In this case, the first driving shaft is driven by the aforementioned tool motor at a low speed, and therefore the first driving shaft, the second driving shaft, and the pivoting shaft are rotated at a low speed.
When the tool support head is tilted, the second driving shaft, through which rotation driving force is transmitted to the tool, and the pivoting shaft, through which pivoting driving force is transmitted to the tool support head, are rotated together at a low speed. Therefore, the composite machining lathe disclosed in patent 2 cannot simultaneously realize a high-speed rotation operation of the tool and a tilting operation of the tool support head. In the power servo motor turret table disclosed in cited patent document 3, in trying to rotate a cutter tool, a cutter tool rotary device related mechanism is driven by a cutter tool rotary device driving motor, and in trying to rotate a turret (a tool unit), a turret rotary device related mechanism (a tool unit pivoting device related mechanism) is driven by a servo motor. The cutter tool rotary device related mechanism is provided in a through-hole formed at a position dislocated from the center of an adjacent convex block. The tool unit pivoting device related mechanism is provided in another though-hole formed at another position dislocated from the center of the convex block. A plurality of passive gears to be engaged with gears of the tool unit is provided around the turret table. Rotation of the servo motor is transmitted to a gear wheel in the turret table through a power transmission bar and a transmission gear. The gear wheel is eccentric from a pivoting axis of the turret table and then engaged with one of the passive gears.